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Phosphate

• phosphate intake
• phosphate functions in the body
• phosphate regulation
• phosphate deficiency

 

Phosphate Intake

An adult has about 600 g of phosphate. 85% is skeletal, with the rest in the ECF and tissues. Only 0.1% of the body's phosphorus is in the plasma.

About 65% of phosphate is absorbed, mainly in the duodenum and jejeunum transcellularly in a process enhanced by vitamin D.

Of plasma phosphate, 55% exists as free phosphate in the form of HPO₄^2- and H₂PO₄^- , which act as a buffer pair.

 

 

Phosphate Functions in the Body

 

Of plasma phosphate, 10% is protein bound, 35% is complexed with ions such as sodium, magnesium, and calcium, and 55% is ionized.

Phosphate is a key component of cell membranes.It is also used to produce ATP and is an essential component of DNA and RNA.

 

 

 

 

Phosphate Regulation

Plasma calcium and phosphate concentrations are close to the saturation point at which calcium phosphate precipitates out of solution onto the bone matrix. Accordingly, plasma values of the two ions are inversely related, as a rise in one will cause a fall in the other.

 

 

Renal phosphate regulation

All phosphate not protein-bound is freely filtered through the glomerulus.

The maximum rate of reabsorption along the nephron is limited, and everything above a threshold is excreted.

Of that filtered, 80% is reabsorbed in the proximal tubules in a transcellular process relying on sodium reabsorption. Apical phosphate entry is controlled by PTH.

There is no significant phosphate transport in the loop of Henle. Distal tubules reabsorb a further 10% and the collecting ducts 2-3% in a manner appearing similar to that of the proximal tubules.

 

 

Phosphate Deficiency